text:
Would solar panels on the wing of an aircraft increase drag?
If a small scale UAV (wingspan <2 metres) was to be fitted with solar panels on its wings to have more power available, would the addition of these panels cause an increase in the drag coefficient, and consequently aircraft drag?
Though wind tunnel testing would be required to ascertain the exact change in drag, can one theoretically anticipate a change in drag on account of these solar panels? Furthermore, will the minimal variation in surface thickness on account of the panels result in the same?
The solar panel thickness is of the order of micrometres.

What kind of solar panels are you thinking about? Of course if they are not as smooth as the wing they will add drag. Putting them under a clear material that follows the airfoil shape will prevent that issue.

I am referring to mono crystalline silicon based solar cells, which are quite smooth. They would indeed follow the airfoil shape. I wish to know to what extent would the drag increase compared to the drag values obtained from simulation softwares such as XFLR5?

By adding drag would you also mean the induced drag that would come along with having heavier wings?  Assuming, of course, that it would make the wings heavier...

I was primarily referring to the parasite drag. I have not considered the possibility of induced drag, as the weight addition would be minimal. Moreover, wouldn't the coefficient of lift reduce which will in turn reduce the induced drag?

It would depend on the airfoil design.  But if the airfoil remains unchanged and weight is added, the AoA will have to increase to deal with it.  And that will increase induced drag so...  But if the weight difference is minimal, I really wouldn't worry about it.

Thanks for your insights! What would you say about the change in parasitic drag, if any at all?

You need to be more specific. If the airfoil contour and surface is not changed, there will be no change in drag. Weight does not play a role here (and in any case, there is not enough information in the question to consider the many factors that might play a role).

The solar panel is being placed on the wing surface. Naturally, it will follow the wing contour. The thickness of the panel is of the order of micrometres, so a microscopic variation in airfoil thickness will be present. Based on this information, can one conclude parasitic drag will increase is my question.

Note that the amount of power gained this way will be insignificant for any craft which is not a glider - about 250W/m^2. It's just about enough to run a hyperefficient car, such as in the "World Solar Challenge".

No, assuming the wing geometry and the coefficient of friction of the material on the surface of the wing do not change. So, swapping a section of aluminum or carbon fiber skin on the wing for a section of Plexiglas or silicate glass under which you place the solar cells will, all other things being equal, have a negligible effect on drag.
However, doing something like this, all other things are not necessarily equal. First off, the border between the normal skin material and the solar cell cannot be a perfectly smooth transition; at some level of magnification, there will be a noticeable seam which will reflect as an increase in the surface "roughness" of the with with solar cells compared to the one without. While nonzero, it's likely negligible if the parts of the wing are well-fitted.
Second, there will likely be a change in mass when removing a thin layer of aluminum, carbon fiber or polymer sheathing, and replacing that with Plexiglas with solar cells underneath (plus the power wiring, converters and other additional components that otherwise wouldn't need to exist). Classically, that has no effect on drag, but it will change momentum calculations which affect how much the drag matters, and also as was stated, heavier masses require higher angles of attack to increase lift and counter weight, which increases induced drag as the effective shape of the airfoil slicing through the air changes to present a larger cross-section. Wing stress moments will also be affected as the weight distribution of the plane between fuselage and wings has changed, and this can change the amount of effective dihedral due to wing loading under various conditions.
Lastly, there will be a nonzero difference in surface roughness between the majority of the skin or sheathing and the solar cells. For instance, a matte finish as some aircraft have is rough by definition to provide different reflective planes to scatter light. You want a highly polished surface on the solar cells to minimize energy loss through the outer layer. Even if most of the aircraft is finely polished, there's a difference in how fine a polish various materials can take; the harder the surface, the easier it is to take a fine polish.


text:
What is the correct holding altitude for the missed approach at Unalaska (PADU)?
On this approach plate, the holding pattern shown is depicted for a missed approach:

However, in the notes, it says to

Descend to 6000 in holding pattern.

even though you should only climb to 4700 feet, according to the missed approach procedure:

Climb to 3000 via 166° bearing then climbing left turn to 4700 direct DUT NDB/DME and hold.

What does the note actually mean (especially since it seems to be implying you would be higher than 6000 on the missed approach procedure)?

That note actually refers to the holding pattern in general, not to the missed approach procedure. Your reading of the missed is correct.

Descend to 6000 in holding pattern.

Refers to descent from the MSA or any other enroute altitude. Before transitioning from enroute to the outbound initial segment (departing the IAF) the pilot must descend in the hold to 6000. Once leaving DUT outbound, descend as specified to 4700.

But would that mean you'd follow the same holding pattern (i.e. direction and side of the NDB)? Because if I'm reading correctly, that'd put you on the opposite direction of the outbound PT, and there isn't anything that says to hold-in-lieu of the PT.

Yeah, I think you would. The KPAE VOR16R approach looks a lot like this, and I've done lots of instructional flights that transition in an unideal way from the hold to the outbound. You're correct that you cannot do a hold-in-lieu-of the PT. Remember that the same question could apply to transitioning from the missed approach to the outbound in any situation!

In slightly simpler terms, the first note that references 6000' is about the approach.  The second note that references 4700' is about the missed approach.

In this approach (and several others in Alaska) you may need to descend in a holding pattern from a higher assigned altitude to one that is used to begin the approach. For example, you might be assigned 10,000 ft. coming to Dutch Harbor from Cold Bay on G8. When you get to DUT, the initial approach fix, you would descend in the holding pattern from 10,000 to 6000, and continue to the procedure turn from there.
As Egid said, it does not affect the missed approach, in which you climb to 4,700 feet and hold at DUT.

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text:
Are conditional line-up clearances still valid if the referenced traffic initiates a go-around / missed approach?
Suppose you are the captain of Big Jet 345:

Big Jet 345, behind landing Boeing 757, line up runway 27, behind
Behind landing Boeing 757, line up runway 27, behind, Big Jet 345

Now suppose the landing Boeing 757 executes a go-around. Does the conditional clearance allow you to line up and wait after the Boeing 757 flies over the touchdown point?

Note: This question pertains to international/ICAO (non-US) procedures.

This may sound obvious, but you should probably ask ATC.
In the sentence given it specifies that you should line up behind the Landing B757, not the Going Around B757. This sounds pedantic, but the situation has changed.
The chances are the ATC is still expecting you to be the next aircraft on the tarmac, but if you're in any doubt whatsoever, do not put your aircraft on a live runway (or anywhere else you can reasonably expect another aircraft to want to be in the next 5 minutes) without explicit, unambiguous permission.

Or unless you have an emergency.

Even in an emergency I'd still inform control of what's happening which is usually phrased as a request but never treated like one. If you declare an emergency and then ask for a runway, you get it unless it's physically impossible

Asking ATC is a prudent course of action. But does the clearance authorize you to enter the runway? I'm guessing it happens pretty frequently.

Probably not as frequently as you'd expect - airliners don't do that many go-arounds, and most major airports (ones busy enough to need to line the next plane up ASAP) use separate arrival and departure runways. The point is that the clearance is, by definition, ambiguous, and you should therefore check.

Europe Answer
In some non-US jurisdictions (such as the UK) it is allowable to issue conditional LUAWs, so the possibility exists that you would have a go-around of the landing aircraft.
I do not fly in Europe, but I assume that you normally only move onto the runway AFTER the landing aircraft has touched down. If the aircraft does not touch down (go around), then the LUAW condition is never met, so you do not move onto the runway. The controller would have to issue another LUAW (or departure clearance).
United States Answer
The example given is not a valid ATC instruction in the United States. A U.S. ATC should NEVER make a "conditional" LUAW. If a tower gives such an instruction, I would confirm it without the illegal conditional. If I heard a tower routinely making conditional LUAWs I would report it, because it is dangerous and a huge violation of FAA departure procedures.
You never line up and wait on the same runway which another aircraft is in the process of landing on, so the "go around" scenario should never happen. If, by some bizarre miscommunication, you think ATC is telling you to LUAW on a runway and you see another aircraft in the process of landing on that runway, you should say "[callsign] holding on [intersection] at [runway #], landing traffic in sight".
Note that it is dangerous and a serious separation violation for a controller to issue a LUAW when another aircraft is cleared to land on the same runway. If you hear a controller issuing such LUAW it should be reported immediately. Any landing aircraft must be landed and on the ground before a LUAW is given to a departing aircraft on the same runway.
If a plane is on long final (but has not been cleared to land), and you are given a LUAW on the same runway, the controller MUST inform you of the other aircraft and how far out they are. You may opt to refuse the LUAW based on that information. Under no circumstances will the other aircraft be granted a landing clearance, until you are off the ground.
If you are unclear about phraseology, you may want to review FAA Departure Procedures.

-1 this is valid ICAO phraseology

In the United States controllers may not issue conditional LUAWs (3-9-4a). Also, the instruction must include the intersection (if applicable) which your example does not.

No intersection is necessary. If you are at the hold bar, it is pretty obvious at which intersection you will enter the runway. The runway itself needs to be mentioned. FAA source: http://www.faa.gov/airports/runway_safety/news/current_events/lauw/

If it is a LAUW at an intersection, the intersection must be named. If it is not intersection, then it can be omitted.

@DeltaLima I have updated my answer to remove the intersection-related comment, since it is irrelevant to the main question anyway.

You are right about the FAA's restriction on the conditional part. See 3-9-4 of this document. I am not aware of this restriction under generic ICAO guidelines.

@Hugh Apparently there is a difference between US and Europe/ICAO procedures. I have updated my answer.

In Europe you don't have to wait for the AC to touch down, just pass your position. As soon as it's by you can line up and wait.

Whether you are a jet or light aircraft the procedure is the same where conditional lining up is permitted. If an aircraft announces they are going around it's not a landing, so it would not constitute clearance to line up. If you think about it an aircraft may announce a go-around before they reach the threshold, and if you line up there's a potential conflict if the aircraft on approach has an emergency.
Also, remember you can refuse a clearance if you're not happy with it. Call ATC and ask for instructions, never assume!

The question clearly says "after the Boeing 757 flies over the touchdown point". Then you can't create conflict any more.

How do you know why a go-around was called? Maybe they broke off the approach because someone got ahead of them. You're better off staying put and asking for instructions.

@GdD: bear in mind that it's only a Line-Up and Wait clearance, not a takeoff clearance, that's being issued in this hypothetical case. So the risk of a collision is pretty low.

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Can you obtain a pilot license with impaired vision / being blind in one eye?
A friend of mine is blind in one eye and has normal vision in the other eye.  Would this prevent him from getting a Private Pilots License in the US?

It's possible to get a special issuance medical certificate in this case:

An applicant will be considered monocular when there is only one eye
  or when the best corrected distant visual acuity in the poorer eye is
  no better than 20/200. An individual with one eye, or effective visual
  acuity equivalent to monocular, may be considered for medical
  certification, any class, through the special issuance section of part
  67 (14 CFR 67.401).

It is both perfectly safe and perfectly legal to fly with monocular vision.
Safe: A classic US Air Force study (that led to a revolution in the study of vision and neuroscience more broadly) demonstrated many decades ago that (a) our sense of depth comes from many sources, and (b) stereo is of remarkably limited utility in many situations -- for example, when objects are much further away than the distance between our eyes, as is the case in most situations while flying. Motion is in many cases far more important. This is extremely well established in the literature.
Legal: as mentioned in a previous answer, monocular pilots require a special waiver for their medical certification. The reason is simple: monocular vision, by itself, is not a biggie; but if you have one eye, it's worth making sure there's nothing else amiss, and that a pilot with recent loss of vision has developed the intuition required to comfortably sense depth with other cues.
Tell your friend to go do it!

From my own experience, binocular vision is critical to depth perception inside about three meters, and almost superfluous in that respect beyond ten meters or so.

Do you have citations to the USAF study?

I was a victim of a virus in one eye that blinded me in that eye.
After a competency check ride with the FAA with vision in only one eye, I am back to flying like I always did.
I have never noticed an issue with flying with vision in only one eye.
Obviously, curiosity set in with me, so I asked around and was surprised to find that many pilots are blind in one eye, and like me, vision in only one eye has not affected their enthusiasm or enjoyment of flying.
I am a commercial pilot, and was informed by my medical examiner that there are many airline pilots who also are blind in one eye. The point is that you can become a professional pilot if you have vision in only one eye.

Just an addition to the previous answer,
While they may be legally able to get a medical cert and complete the training they may find it extremely difficult. Having vision in only one eye can have a drastic impact on depth perception and ones ability to observe motion. The human body can see distance, and motion (distance change over time) largely by triangulating objects from both eyes. If the loss in vision happened later in life many people are able to retain enough estimation ability to still be able to see and estimate motion and distance with ease. While I would advise him to give it a try he may find certain things very difficult and he should be prepared for that. I would also strongly advise an instrument rating in this case so as not to need to rely on vision all the time.

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text:
What are these painted lines on the fan blades of the Rolls-Royce Pearl 15?
I'm not sure that they are painted but it looks like they are. What are they for?

More images:

It looks like they end a bit for the edge of the blade. Could they be for judging the wear of the blade, i.e. something like "if the line touches the edge, the blade needs to be replaced?"

@JörgWMittag most definatly not wear indicators. If your fan blade rubbed enough to wear that much you have serios problems. Hard to see if they are 3D or not in these pictures, but I would guess either some sort of alignment mark for manufacturing if they are 2D, or a turbulator of some kind if they are 3D.

This is what I love about aviation: every single piece has a meaning and serves a purpose. Always. If those lines were on a car, everybody would assume they are just decoration.

I just sent an E-Mail to the E-mail addresses that found in these two pages of Rolls Royce company. Hope to get answer.: https://www.rolls-royce.com/products-and-services/civil-aerospace/business-aviation/pearl-15.aspx#section-contacts and https://www.rolls-royce.com/products-and-services/civil-aerospace/airlines/br715.aspx#section-contacts

Expanding on the answer from user14897, these roughness strips work like the dimples on golf balls. They trip the boundary layer from laminar to turbulent, which helps keep the flow attached. A turbulent boundary layer means more skin friction, but the added flow speed and momentum close to the surface helps it overcome an adverse pressure gradient and stay attached.
Usually turbulent flow means higher drag than laminar flow, but separated flow causes much higher drag than attached flow, be it laminar or turbulent.

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text:
Is a CFII required in order for a flight Instructor to provide training for added class ratings?
Must a flight instructor have a CFII to provide multi-engine add-on training to a customer meeting the following criteria:

Holds a commercial pilot certificate with a single engine land class rating.
Holds an instrument airplane rating.
Holds a valid medical certificate.

So, put plainly, our hypothetical customer holds a commercial pilot certificate with a single engine land class rating and an instrument rating.  He/she has a "single engine commercial-instrument ticket" to use industry lingo.
Does the customer's MEI have to have a CFII to give the add-on training?

I can appreciate the logic in your answer.  I don't know if I fully agree as there are instrument ACS requirements that have not been evaluated by the DPE.  Namely, a SE ILS approach and SE instrument maneuvers.  See page A-7 of the instrument ACS.  I would imagine a CFII is required to sign off saying the applicant is prepared for those otherwise the applicant would get a ME VFR only limitation on their certificate.

@wbeard52 - Thank you for the comment. I invite everyone to try to poke holes in my arguments so that I can sharpen my arguments or abandon them. The ACS does not specify training requirements or who must give the training, only that certain skills need to be evaluated for the issuance or a certificate or rating. Part 61 governs training and airman certification.

My OPINION on this whole thing, which is just one guy's opinion:
An instructor need not be a CFII to provide training for an additional class rating to an existing instrument pilot with a category rating under which the additional class falls.
If a customer already holds a commercial airplane certificate with a single engine class rating and instrument airplane rating, an instructor does not need to hold a CFII to provide training that customer’s multi-engine class training.  My regulation walk is laid out below.  Please read it before voting or commenting.
Important note: if the customer is NOT instrument rated and is seeking the instrument rating for the category -and/or- the customer is seeking to upgrade from a PPL to a CPL or CPL to ATP, the instructor must hold a CFII/MEI.
Regulation Walk
First, when is an instructor required to hold a CFII?
61.195(c) outlines instructor limitation and qualification related to the instrument training.  This reg specifies that an instructor must be a CFII to provide instrument training for the issuance of an instrument rating, a type rating not limited to VFR, the commercial certificate, and the ATP certificate.
If we stop there it sounds like an instructor needs to be a CFII to provide training to a customer seeking a simple ME class add-on to an existing airplane SE comm-inst.  But wait…
Are we really conducting “instrument training” while preparing for an additional class rating to an existing SE comm-inst ticket?  No, we’re not.  “Instrument training” has a definition in 61.1:

Instrument training means that time in which instrument training is
received from an authorized instructor under actual or simulated
instrument conditions.

61.1 also defines “flight training” which is different from “instrument training":

Flight training means that training, other than ground training,
received from an authorized instructor in flight in an aircraft.

The training for an additional class rating to an existing airplane SE comm-inst is not “instrument training,” it is flight solely by reference to instruments and that’s an important distinction.  It sounds pedantic, but the FAA intentionally uses these two terms very carefully:
61.109(b)(3) – PPL airplane multi-engine aeronautical experience requirement

3 hours of flight training in a multiengine airplane on the control
and maneuvering of an airplane solely by reference to instruments,
including straight and level flight, constant airspeed climbs and
descents, turns to a heading, recovery from unusual flight attitudes,
radio communications, and the use of navigation systems/facilities and
radar services appropriate to instrument flight.

61.129(b)(3)(i) – CPL airplane multi-engine aeronautical experience requirement

Ten hours of instrument training using a view-limiting device
including attitude instrument flying, partial panel skills, recovery
from unusual flight attitudes, and intercepting and tracking
navigational systems. Five hours of the 10 hours required on
instrument training must be in a multiengine airplane.

Do you see the difference?  It’s carefully written to allow a non-CFII to conduct PPL ME training but requires a CFII to perform CPL ME training (which is also true for CPL SE).  But wait, there’s more…
61.109 and 61.129 are aeronautical experience requirements for the PPL and CPL certificates.  Note that our customer already holds a CPL certificate for airplane SE and an instrument airplane rating.  The instructor does not need to meet the hour requirements in 61.129 because 61.63(c)(3) [Additional Class Ratings] gives us:

A person who applies for an additional class rating on a pilot certificate…need not meet the specified training time requirements
prescribed by this part that apply to the pilot certificate for the
aircraft class rating sought; unless, the person only holds a
lighter-than-air category rating with a balloon class rating and is
seeking an airship class rating, then that person must receive the
specified training time requirements and possess the appropriate
aeronautical experience.

This means that no “instrument training” is required and that any training that takes place is “flight training solely by reference to instruments” and can be performed by a MEI without a CFII.
So, to conclude…
…a customer seeking to add a ME class rating who already holds a commercial pilot certificate for single engine land airplane with and instrument airplane rating is not receiving commercial certificate training because he/she already holds a commercial certificate.  They're merely adding another class to their commercial certificate.
…a customer seeking a ME class rating who already holds a commercial pilot certificate for single engine land airplane with and instrument rating is not receiving instrument training because he/she already holds an instrument airplane rating.  Again, just a class add-on, not a new rating.  There are no ME or SE instrument ratings, it's a category rating.
…the training received is purely multi-engine operation training and covers how to exercise the privileges of their existing commercial pilot certificate and instrument airplane rating while flying a multi-engine airplane.  It is not training for an instrument airplane rating (they already have it) and it’s not commercial certificate training (because they already have it).  It’s an additional class rating per 61.63.
…our CFI/MEI (no CFII) can give the training and endorse the customer for a practical exam.
Important notes:
A customer seeking to upgrade a cert from PPL to CPL -or- CPL to ATP must receive training from a CFII/MEI.
A customer going for an initial instrument rating must receive training from a CFII/MEI.


text:
Does the US military use metric system?
Does the US military use the metric system for aviation?
For example, does it use:

feet or meters for altitude?
nautical miles or kilometers for distance?
knots or km/h for speed?
inHg or hPa for pressure?
°F or °C for temperature?

If so, how do they work with ATControllers who are used to using customary measurements?

If they did, they would be brave, but quite isolated with China and Russia, and North Korea, though they would be very right.

"customary measurements" is a very odd turn of phrase to refer to the old-fashioned "imperial" system of feet and inches etc.!

@MikeB Actually, there is a difference between imperial units (commonwealth feet, inches, etc) and U.S. customary units (U.S. feet, inches, etc).  Part of the drive for standardization was that the length of feet and other units were different in different parts of the world.

As the US military primarily flies and trains in US airspace, they use the standard measures associated with the airspace. That is feet (or flight levels), nautical miles and knots, inHg, and °F. Though, using °C is fairly common in the US now since weather reports shifted to the ICAO format.
That said, the cockpit systems can be switched to HPa and meters for altitude and °C for temp for when they fly in airspace where that is the standard. Speed and distance are always in nm and kts.

Do you have any sources?

@Zaz  Personal experience. Retired USAF. Private pilot and twenty+ years of avionics development since then.  As I indicated, electronic displays make switching a relatively minor issue.  Temperature and Pressure seem to be migrating to metric just because of the ICAO weather standards and it's not a real impact. Who cares whether the altimeter setting is 1011.0 or 29.90? Altitude is driven by ATC and the airspace. See airspace description in the AIM. Speed and distance are Kts and nm, and of course there is Mach.

Since 1955 when I first soloed a flying machiine  I used FEET to reference my altitude. Now 63 years later and over 30,000 hours I still do. This of course is mainly due to the altimeters in the U. S. are calibrated in feet. I own several examples of metric altimeters. WWll Japanese, WWll German and current design Russian altimeters that indicate altitude in meters and Km. Just for grins I've carried them on board while flying VFR. What I found is that our altimeters graduated in 20, 100 & 1,000 foot increments are more sensitive than the metric, being 300 feet ≈ 100 meters for each major altitude graduation.
From an ancient pelican

"our altimeters ... are more sensitive than the metric" - Nonsense. The scale used has nothing to do with the sensitivity.


text:
Why do two similar planes with the same engine have such different performance?
Why do two similar planes with the same engine have such different performance? For example, the Ikarus C42 and the Eurofox both use 912UL engines, but the Eurofox cruises 15 - 20 knots faster.
What factors contribute to this?

Do you have a source about the powerplant and the maximum speed of the Eurofox? According to the official website, the Eurofox can be powered by a Rotax rated either 80, 100, 115 or even 141hp but the relevant max speed is not given. For the Ikarus those values are listed but without the correct couple powerplant/max speed of the Eurofox, any answer would merely be speculative...

@sophit the Eurofox POH (available on their website) states speeds for each engine. I am talking about the 80HP 912UL (not the "s") - as that's what the C42 has

Do you have a link?

@sophit I googled "Eurofox POH" for you - bottom of this page: https://eurofoxaviation.co.uk/factory-built-microlight

Perfect, thanks

Wing loading -- mostly wing area because these aircraft have essentially the same gross weight.
The Ikarus has almost a 20% larger wing.
For these aircraft, the drag polars will be substantially similar.  Importantly, the lift coefficient for best L/D will be about the same.  This means that the cruise lift coefficients will be about equal.
The definition of lift coefficient in level flight:
$C_L=\frac{W}{q\,S}$
Can be re-arranged
$V=\sqrt{\frac{2}{\rho}\frac{W}{S}\frac{1}{C_L}}$
Dividing this expression by itself (but applied to airplanes 1 and 2), then cancelling all the constant terms.
$\frac{V_2}{V_1}=\sqrt{\frac{S_1}{S_2}}$
Plugging in numbers...
$109\times\sqrt{\frac{135}{112.5}}=119$
Which is pretty close to the 120 claimed.
I would expect the Ikarus to have better stall speed, takeoff distance, and landing distance -- unless the Eurofox uses more sophisticated high lift devices.
Note, the Wikipedia article for the Eurofox has a metric to standard conversion error on the wing area.  Correct value used above.  10.45 m^2 is 112.5 ft^2.

Thanks Rob. Is the wing size on line 2 a typo? Does the C42 have a smaller wingspan?

@Cloud Line 2 of what?  The wing areas I saw on Wikipedia were 135 for the Ikarus and 112.5 for the Eurofox.  That is a ratio of 1.2.  Bigger wing, lighter wing loading, slower airplane.

So the larger the wing ratio, the slower the plane?

All else being equal, the larger the wing, the slower the plane.  In these equations, S is the wing area.  W is the gross weight.  W/S is the wing loading -- since S is on the bottom of wing loading, it behaves opposite.  Light wing loading (small W and big S) is for slow airplanes.  High wing loading (large W and small S) is for fast airplanes.


text:
Is there any mechanism in engine mount to prevent shock loads on engine while landing?
How engine is mounted in wing is restricting motion in any direction but is it still resistant to shock loads, or is there any mechanism inside engine associated to bearings that will absorb shock loads that occur in spools?

Related Thrust bearing. Engine spools already experiment axial loads in flight, due to the unbalance of forwards and rearwards thrusts inside the engine. Thrust bearings are used to resist this unbalance and maintain the spools in place.

The wing joint also absorbs a lot of the landing impact as the wings flex down, either at the wing joint itself or if the gear are mounted in the wings there. It may help to understand that the wing is not a rigid system, so I wouldn't really qualify it as a "shock load". Aside from that the gear damping mechanism takes a lot of the "shock" from landing as well, so not a lot is transferred to the engine. This may be more of an issue for turbofans that have gear mounted in the nacelles.

@ron beyer, there are cases which we find bearing ball indentation in bearing races, especially on outer race roller path. btw it is a low bypass turbofan so shock is comparitively more while landing. how about commercial aircrafts? is this the same case on high bypass too?

This may be interesting to know if aircraft landing with arresting systems are specifically hardened.

@Ron Beyer your comment is an excellent answer. Shock absorption (stretching load force over greater time) can be accomplished from the wheels on up to wing flex.  The entire engine would experience landing "shock" (as would passengers) as long as there is not any gap in the bearing. (It would be designed to handle the same G loads as the rest of the plane (with adequate safety margin)).

@Anso Mamachan. It is possible a heavier/larger engine redesign has left some other component deficient in strength.  I would make sure the ball bearings were in spec first (they could be wrong alloy/improperly tempered), also local operating temperature deviation (improper lubrication).  It would be good to know the engine it was happening with, and how often.

"Shock" loads on landing can be transmitted to engine components.  The original poster appears to be asking about turbine engines specifically.  The significance of a hard landing on the engine spools themselves will be shaft flex and case flex, and the possibility of blade rubbing (and erosion).  This is a concern with a hard landing, and something that must be considered.  There are not "shock absorbing" features or capabilities built into bearings in engine spools; these are intended to have minimal friction in rotation, but no concentric movement about their axis.  It is possible in severe turbulence, and in a hard landing, to experience case or blade damage or wear, and there are inspections prescribed for certain components in certain engines to address this.

Back in the early days of the deployment of the C-5 cargo plane, overflexure of the wing-to-fuselage attachment during landings was identified as one reason for the serious cracking in that area which the first revision of the C-5 was susceptible to.
One cause of the overflexure was that during a hard landing, at the moment of touchdown the mass of the engines and the wing itself would sag the wingtips downward as the landing gear was absorbing the shock loads.
One of my engineering professors was involved in a design exercise to study the feasibility of a thrust-vectoring system which, upon touchdown, would briefly deflect the engine exhaust downwards to lift the engines and wing upward and limit the downsag, and thereby extend the fatigue lifetime of the wing-to-fuselage attachment.
To my knowledge, nothing ever came of this proposal- but it represented a case where shock loads on the fuselage caused by the inertia of the engines needed to be managed.

There are no mechanically significant shock loads on an airplane engine in normal operation.

adding some detail and references to your answer will keep the predators away.  Your answer is generally correct.


text:
What possible causes can there be for a crash in good weather conditions?
The preliminary report for the TNFlygirl crash says:

About 1019, the airplane entered the first of a series of climbs and descents with
corresponding fluctuations in its observed groundspeed. During these oscillations, which
varied in magnitude, the airplane’s altitude varied between about 6,400 ft and about 5,300 ft.
About 1057, the airplane entered a descent that arrested about 4,300 ft at a groundspeed of
143 kts, after which it climbed to 6,050 ft and slowed to 85 kts. The airplane then began to
descend rapidly before ADS-B contact was lost in the vicinity of the accident site. During the
last several seconds of the flight, the airplane was on a ground track of 262° descending at a
groundspeed that reached a maximum of 228 kts, and the estimated maximum descent rate
was about 11,900 ft per minute.

Now I'm not asking what the cause of this crash was as that would be speculative and off-topic, but I am interested in what sort of things could cause a pilot to essentially nosedive into the ground on a clear VFR day with low winds.
This incident was not a stall or spin one, so I don't even have an idea of what kind of things could cause this to happen and would like to know for future reference, and to honour the pilot in question by at least taking away some valuable lessons from the incident.
Further viewing / preliminary analysis here and here.

Note to answerers: Any speculation on the cause of the linked accident will be removed. We do not speculate on ongoing investigations here.

Your second link gives one possibility that could certainly apply to other accidents.

Note to commenters: If you comment on the cause of the linked accident that will also get removed.

I’m voting to close this question because it's inviting speculation

Icing could cause it. https://www.youtube.com/watch?v=6_3b9DTrGXs

Usual immediate cause is failure of one or more components (including crew as "components" here).  However, the purpose of an investigation is to find the underlying root cause.

How is that different from Asking simply 'What possible causes can there be for a crash, other than weather conditions?'

A few things come to mind:

Partial or full pilot incapacitation. Anything from a heart attack, or stroke, through to hypoxia could make a pilot lose control and crash. Illness does not care whether the pilot is in VMC or IMC.

Spatial disorientation. Sounds unlikely on a clear day, but it's fairly easy to fixate on one thing (possibly a problem in the cockpit) at the detriment of almost everything else. There's a reason we're drilled Aviate, Navigate, Communicate!

In-flight fire. Even a minor egress of smoke or fumes could either distract or disorient a pilot to the point of crashing. A full-blown fire could disable crucial controls or the pilot.

Mechanical failure. The failure of a crucial component such as the elevator could lead the pilot to lose control and crash

Basically, you're asking "What are all the reasons one might crash in fair weather" and that's a pretty vague and broad question, bordering on off topic.

Let's not forget the all too common collection of pilot actions that can be summarized as "Stupid Pilot Tricks."

Also add to the list, the rare, but possible: suicide by pilot.

Wouldn’t bird strikes be another possible cause of fair weather crashes? Also pilot and/or ATC error(s)?

Plastic particles in the fuel truck. (Real story, but they managed to save the plane despite stuck throttles.)

@ToddWilcox, bird strikes are rare at altitude.  Yes, there was that vulture that got hit at 37,000 feet, but the majority take place within a hundred feet of ground level.

For now, let it be a cautionary tale about trying to fly too close to the sun by buying a complex aircraft with only 100 hrs of flying time. Only the military can get away with that sort of stuff because of its tightly controlled and concentrated environment.
It's good that you've had the experience of mental saturation, and understand the need to absorb and internalize aviation's unforgiving nature in baby steps.
Lots of us have this poster on our walls. "An even greater degree than the sea" is mainly because of the added 3rd vertical dimension to the Ways To Get Yourself In Trouble.
I used to teach float ratings. Seaplane ops add a lot of off-airport, exposure-to-the-public, and boating hazards to the aviation stuff. I always started off my initial briefing with:
"Floats is easy to master. It's a big, stable catamaran, wants to point straight, easier than taildraggers really. The hard part is staying out of trouble."

Are you referring to the FAA definition of "complex" or a more generic definition?  (i.e. autopilot, electric trim, etc.)

Airplane with retractable gear and constant speed prop mainly. That's the FAA definition no? And she had to get an endorsement for it in the US? Not required in Canada so I'm not totally familiar with the requirements. The vids of her's from a year before confirmed she was hopelessly in over her head, and her instructors were useless wimps who just pushed buttons for her.

I mean no disrespect to Captain Lamplugh, but to be "in danger" means nothing more or less than to be in a situation that affords you few options for escape without harm, and that's precisely where you are if your situation is "unforgiving of any carelessness, incapacity, or neglect."

@SolomonSlow Standing on the beach near the ocean is not inherently dangerous.  But if due to carelessness, incapacity, or neglect, you continue to stand there when a tsunami warning is sounding you will soon find a situation that affords you few options for escape without hard.

@Michael, I agree. Lingering on the beach while a tsunami approaches is dangerous.

@SolomonSlow Aviation stands out because the medium is 3 dimensional, and time from happy to sad can be so short.

In my opinion the most probable root cause for any of this type of crashes would be insufficient experience.
This can be broken down to four subcategories:

Low overall hours. In this case the pilot simply hasn't accumulated enough experience to fully manage the plane, maybe even the most basic aspects of flight.

plane/pilot mismatch. The pilot may be proficcient as such, but not familiar with the specific plane or equipment he/she ends up using.

"Shallow capabilities". The pilot may perform excellently in normal conditions, but simply has not (been) trained to manage adverse circumstances such as those listed in Jamiec's answer.

Holes in the cheese. The pilot may have been trained poorly,leaving hidden but often critical gaps in knowledge/abilities.

This is flying (pun intended) very close to speculation on this specific accident.

I disagree, it's the other way around: the specific accident just, sadly so, happened to manifest some of the things I listed ... I'd rather have the reference to the accident edited from the question, since it to certain extent limits the answers.


text:
Is it safer to do a regular approach than a short approach?
All things equal, from a standard traffic pattern at a towered airport, is it safer to do a short approach when approved by tower, or a normal one? Assume a Cherokee, Cessna 172, or similar small trainer.
My gut is a short approach should be safer, because I stay closer to the airport in case something goes wrong and I can let up on the decent rate if I hit unexpected wind shifts. However, I descend at 1000fpm in a slip, instead of 500fpm with my nose pointing to the runway. The workload also tends to be higher because there is less time.

If your slipping 1000fpm to do a short approach, I do not want to be your passenger.

The safest approach to a normal landing is a stabilized approach, so it's going to depend a lot on you, your aircraft, and the day's conditions. If you're operating in a confined area, then that changes things a lot, and I'm not going to address that.
It also depends on your definition of a normal pattern and approach. The FAA recommends you fly your downwind around ½ mile to 1 mile from the runway centerline, which should keep you fairly close to the airport anyway, and you should be turning base at least ¼ mile away from the runway threshold.
That said, a normal approach is going to be much safer. As you point out in your question, a short approach often requires extreme descent rates or slips (or both), and results in a much shorter final; neither of those situations improve safety. Approaching with a high descent rate just so that you can reduce it if necessary doesn't strike me as a particularly good choice for normal operations, either.

+1 - IMHO short approaches are fun (and they can be a nice opportunity to do an engine-out simulation all the way to a landing), but a normal (ideally stabilized) approach is inherently safer than "Sure, I'll chop my throttle, slip like crazy to drop the altitude, and challenge myself to make it a spot landing just to keep it interesting!"

I agree that a normal, stabilized approach is the safest. However, if the conditions, pilot experience, and the airplane permits, short approaches can save a lot of time and fuel (cost) as well as expedite traffic for all concerned. The same can be said, although in a more limited manner, for unstabilized approaches.

There's a happy medium between a 180 power off approach abeam the numbers, and flying a 1/2-1nm Faa-approved approach, and that is to be continuously in a position to land from the entire approach in the event of an engine failure.

Oh, this one is hard to answer, but let me have a try:
There will be no universal answer as it is very dependent on

How likely are certain emergency situations to happen
The Runway available
Terrain below (obstacles, landingsights outside the airport, populated area or not)
The aircrafts characteristics (ofcause we are talking only of SE)
You

and most probably even on some more.
Your chances to get to the 'safe' runway should you encounter an engine failure are much bigger and you will also be faster on ground in case of fire if you remain close to the field - both emergencies are very remote but allways to consider. I take them into account when planning to fly over Water or over congested areas according to FAR 91.119

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
  (a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
  [...]
  FAR 91.119

A traffic pattern is obviously a maneuver necessary for takeoff and landing. But you are not asking about legal facts but about safety, so let's go ahead.
We found out that a closer pattern will most probably give you the best chances if you have an engine failure or fire and there is no other safe spot to land then the runway. But that's not completely true because if you compare a 'normal' to a short approach ~70% of the pattern (~90% of the engines workload) will be exactly the same which even makes an engine failure or an fire on board more remote to happen during the phase of flight where you are closer tomthe runway as 'normal'.
@Egid mentioned a stabilised approach,  which results in a lot of safety. He even called it the safest way to fly an approach - guess what my comment on this is, right, start reading at the top: it's dependent on blablabla ;) All right man, you're answer is basically correct and I practice it 90% of my landings but the runway available and obstacles sometimes make me think a different way. Assuming a short muddy grass strip : Stop talking about extra safety thanks to a short approach - suitable words were either funny or risky. Also a stabilised approach until 50ft would not be my first choice.  If I would approach this runway with nothing else in my mind than maximum safety I would chose a little longer final than usual, stabilise the airplane early - final configuration, all checklists done, on spped on glide path on centerline - but after clearing the obstacles deviate from the approach path to do a short field landing optimally with the aircraft fully stalled at touchdown on threshold.
There are aircraft you either fly stabilised or better leave on ground. An example would be the Cirrus aircraft, but honestly I have not enough experience on them to really consider them to be not suitable for steep dives into final. Anyway these and other agile aircraft are much safer to operate the 'normal' way.
I'm also a huge point to consider.  If I would sit there with the hands on the controls flying not further than a quarter mile from the runway afraid of my engine going off any second, I would rather visit the doctor but don't go flying.  There are these days where you are concerned of anything, check everything 3 times and take some extra precautions wherever possible. But then I've checked everything but my self prior this flight. You won't perform well if you are afraid of what you are doing.
But I don't think that you are someone who's afraid but someone who wants to do his best to fly as safe as possible - a pilot who thinks that way he's supposed to do. But you're still a factor. Ask your self if you are familiar enough with the aircraft, the approach, the situation and feel comfortable to cut it short if you like to do so. Consider that there will be a higher workload (work / time) you will have to manage.
All in all you need to think of a lot off points and I myself come to the result that I would brief and fly the approach I feel most comfortable with - easy isn't it? ;)


text:
Do GA pilots routinely request "flight following" from ATC, and why?
My understanding is that private pilots are able to contact air traffic control and request "flight following", as it may help them with their situational awareness. Beyond that, however, I'm curious:
Is this a common procedure? What sort of "situational awareness" benefits can be realized by a "flight following" request? What are other pros/cons of such a request?

Thanks for the responses, all. I misread a meta post earlier, and I was going to hold off on marking an answer, but I understand better now that I should feel free to mark the one I found most helpful. I appreciate everyone's willingness to share their knowledge! Thanks again!

I typically like to get VFR flight following if I haven’t filed a flight plan for longer distance flights. The biggest advantage here is that somebody knows where I am if something should happen.
I don’t typically find the chatter too bad, but you do have to be on the ball, especially when handed off from a local airport to an Air Route Traffic Control Center (commonly referred to as just “Center”) frequency. Often on flights out of my airport (KGRB) I will get handed off to Minneapolis Center, which is relatively busy frequency.
Another nice thing is that it gives you some practice talking in busy airspace. You really have to follow the rules and jump in when able. Sometimes they won’t hear you because you are transmitting over other aircraft that you can’t hear, so the frequency will appear open. It’ll sound like they are talking to themselves.
So here is how I see it:
Pros

You are talking to somebody and working with other traffic in the airspace
You are on a frequency you can broadcast an emergency to. Yes we all know about 121.5, but you are not guaranteed to get somebody on the other end.
ATC knows where you are, and if you fall off the radar and don’t respond, they will initiate a search. If you just file a VFR flight plan they won’t even start until 30 minutes after your planned arrival, and then they start calling airports and contact numbers, then start a search. They may not know where you fell off your flight plan so the search area is much bigger.
They can help route you around active MOAs, TFRs, and other airspace/weather issues that don’t show up well on paper maps.
Traffic advisories (as others pointed out)
Can provide a vector to where you want if you get lost.
Don’t need to open a flight plan if you can get following all the way.
Good radio practice

Cons

Flight following is “workload permitting.” They may call up and say Radar services terminated; squawk VFR at any time, turning your flight back into normal VFR. If you didn’t file a flight plan, now you should call up FSS and open one en route, which is more difficult.
Requires you to be on-the-ball with your radio transmissions on busier frequencies. If you frequently fly from uncontrolled airspace, this can be intimidating.
You may get vectored around a bit, but I usually don’t have that problem. I’ve typically contacted the destination airport by 20 miles out and either got clearance or vectors anyway.

Thanks for the thorough answer! Follow-up: As someone who isn't yet licensed, I was surprised to read that 121.5 (a frequency I had come to understand as "someone somewhere is listening for emergencies here") won't always have someone on the other end. Is it common for that frequency to be unmonitored in an otherwise active airspace?

Most towers monitor it as well as FSS, and even some high flying airliners, however that doesn't mean you are going to get a response. If you are in a really remote area or don't have line of sight to a receiver, you may go unheard. Also, if  you do get a response, they still may not know where you are, especially if you don't know (or are too busy to tell). Remember, flying is Aviate, Navigate, and Communicate, in that order. A lot of times you may not have the ability to call for help because you are flying the plane first.

I might make a little more of that last con. The quid pro quo of flight following is that they're keeping an eye on you, a VFR flight, on top of all their IFR traffic, so in return you're expected to help make things a little easier overall by letting them route you around IFR traffic instead of the other way around. How likely they are to do so depends on the volume of nearby traffic; inside a Mode C veil around busy airports, expect quite a bit of it. In smaller cities with less overall traffic, not so much.

It is called "VFR Flight Following", and it is a common and recommended procedure.
Personally, I request "Flight Following" on longer flights, when carrying passengers, or anytime I'm not 100% confident.
When I'm just flying myself in good conditions, I don't bother with Flight Following.
The Pros:

They help with traffic advisories, calling out what traffic you should be aware of.
You're already on a frequency talking to someone, in case an emergency should occur.

The Cons:

It can sometimes be a lot of chatter in your ear, especially if my passengers want to chat.
They expect you to maintain your requested flight; if you go zig-zagging around for sight-seeing reasons, they'll ask for your intentions a lot, or warn you about being off course.

For another good question on the topic, see this post

Thanks for the concise response. I'm going to leave answers unmarked for a while longer in case anyone else has more to chime in with; seems like you guys like to give 24 hours on this SE?

Well as you pointed out, flight following is beneficial as it integrates you in with the flow of other controlled air traffic and, as ground controllers are tracking the progress of your flight, they can provide you with better situational awareness of traffic, weather, TFRs, newly introduced NOTAMs and also provide an additional resource in case of an emergency.
Flight following is not always available to a VFR pilot in controlled airspace, depending on controller resources available for traffic on flight plans.
One disadvantage for requesting flight following, particularly around major commercial hubs eg KLAX, KATL, etc, is that GA airplanes will often be vectored in order to conform with a controller's preferred traffic flow, which may add additional time onto a flight, even when the intended destination of your airplane is not within that airspace.  This is one of the major reasons that pilots on VFR flights often don't contact controllers near Class C or Class B airports or run under the shelves of their airspace.  This was the case with JFK Jr's aircraft on the night that it crashed - not due to a failure to request flight following but done so as a means to expedite their trip to KMVY.

Is there a recommended source for more relevant info about JFK Jr's flight?


text:
Can a commercial airliner be landed on a highway, e.g. Highway 405 in Los Angeles?
In a famous sequence from the TV show 24, a Boeing 727 is forced to land on the 405 in Los Angeles. It is a well-known myth that the interstate highway system was set up as a series of airstrips. But would it be feasible to land a commercial airliner on the 405 highway from an aviation perspective, given that there were few if any cars on the road? (Of course, anyone who lives in LA will tell you that there is never a time of the day or night when the 405 is not busy - so this is purely theoretical.)

Hollywood faked it - 405 the movie

If Dan's link doesn't work: Here is the Wikipedia page. And here is the YouTube link

It's possible, assuming the section chosen has no streetlamps, signs, overpasses etc. The police can block the traffic easy enough.
However, there would be zero reason to do so. If a plane has enough control to reach the highway, and enough advance notice to find a suitable part and block the traffic then it has enough control and time to reach one of the many airports in the region. Much less fuss for all concerned, and a much better equipped crash service.
In the prairies one could set up a fighter or bomber base on a random road, but again there's no need to - there's nothing nearby that would require it, heavy bombers or commercial planes would quickly destroy a normal highway and fighters could use the many civil airstrips in the area.
In Europe the math is different - opponents are a short flight away and destroying the airbases on both sides would be a top priority in any European conflict. See "Highway strip" in the usual reference for more details.

what would the usual reference be?

@Federico wikipedia I guess

You aren't accounting for the weight of the craft and the impact of it landing on the ground.  I don't have any numbers on it, but I'm pretty sure most roads are not designed to withstand the force of a 727 touching down.  The surface could crack in cases of concrete or, in cases of asphalt, the planes gear could possible even punch through.

Notice I said "heavy bombers or commercial planes would quickly destroy a normal highway". And a 727 isn't all that heavy.

@paul the USAF had extensive plans for basing SAC bombers on the US interstate system, using overpasses as parking areas for SAM batteries, fuel bowsers, crew quarters, etc. and the highways themselves as landing strips, taxi ways, parking spots... Whether those plans were ever tested I don't know, I do know SAC detachments tested forward deployment to unprepared salt lakes several times before stopping the tests so as to not give away their dispersal locations to Soviet satellites.

@JayCarr Landing a 727 repeatedly on a highway would wear it out quickly. Doing it once seems unlikely to do much damage, though, if any at all. Consider that a normal tractor-trailer truck weighs up to 80,000 lb., almost exactly equal to the empty operating weight of a 727-100. And that's not even counting multi-trailer trucks. Of course, the 727 would have more weight per wheel. I'm not sure if the 727 can do it or not, but many jet aircraft can actually be landed on grass strips.

@reirab good point, though I'd also point out that semi trucks aren't descending out of the sky when on the road (which makes the force considerably higher...there's another question that covers this somewhere.). And, grass/dirt strips aren't as brittle as concrete, or even asphalt.

@JayCarr That depends on how you land. A short-field landing will apply a lot more force, while a soft-field landing will apply an initial touchdown force less than the weight of the plane.

Citing Wikipedia as reference? okay then.. see "Southern Storm" about Southern Airways Flight 242. Highway landing is a bad plan, even in a rural area. Sometimes it isn't the worst plan.

Maybe not the 405, but some roads in other countries where designed with usage by aircraft in mind.  IFIRC the autobahn was originally designed with that in mind, and NATO has conducted exercises using the autobahn as a runway.  There are some videos on YouTube showing this.  Also, there are videos of other countries using roadways for runways.  Parts of some roadways in Canada and Alaska have turnouts to allow aircraft to be parked after an off-airport landing.
But, back to landing an airliners on the 405.  The 405 has too many light poles and other obstructions that would get in the way.  The strips of roadway used in the videos are devoid of these obstacles.

Here's a Hercules taxiing on the autobahn. As the answer says, there are roads designed for this. Sweden is another typical example of this; the Saab Gripen (as well as its predecessors) are built to operate on 800m long straight sections of road — no expectation of being able withstand a Soviet attack, so why not have guerilla warfare with aircraft from improvised bases?


text:
How do pitch attitude, airspeed and sink rate come into play in a rapid descent or a dive?
So, I have a hypothetical aircraft that needs to get from FL350 to 10,000' as quickly as possible.

What is the difference in sink rate between a 'standard' airliner rapid descent (idle thrust, extended spoilers, and nose slightly down) vs. having the flight crew simply point the nose down below the horizon as far as they care to?
How does the airspeed build-up over time differ between a 'standard' rapid descent vs. a dive?
For a rapid descent, what nose-down pitch would be typical?

Airspeed control is the difference. In a rapid descent, airspeed is controlled and the pilots will keep it below $v_D$, the maximum dive speed for which the aircraft is certified. For a modern airliner, this is somewhere around Mach 0.9.
In a dive with "nose down as far as they care to" (I read this as 90°), airspeed is not controlled, but an outcome of the situation. The airliner will go supersonic. It is possible to recover it from a short dive, but will incur damage to the aircraft (e.g. the pilots will need to lower the landing gear to increase drag, but lose the gear doors in the process).
If the pilots would only care to put the nose down to the point where they not exceed $v_D$, we are back at a rapid descent. They could lower the gear in order to increase the sink speed, and circle to increase drag further. Circling needs more lift (proportional to the inverse of the cosine of the bank angle), so more lift-induced drag is produced. To maximize drag, the pilots should fly at the maximum permissible load factor (which is rather low at maximum dive speed due to gust loads).
If we assume the L/D of the airliner to be 5 with gear and spoilers deployed, the pitch attitude would be between -11° and -12° and the sink speed would be between 50 and 60 m/s (10,000 to 12,000 ft/min). The bank angle would be between 45° and 60° and the plane would be violently shaken by buffeting.
Going any steeper than that would only be attempted by pilots with suicidal leanings. Flying like described above is scary enough already.

I was not mandating that they push the nose all the way over to dive, but you hit the nail on the head here.  Thanks!

Mmo (maximum operating mach number) is not based on structural considerations, but aerodynamic ones.

Also, in combat aircraft, maximum dive speed also has an altitude floor, based on the flight path at a certain number of Gs and not hit the ground.

Might be worth elaborating on the reason why circling helps increase drag (i.e. higher load factor -> more lift -> more induced drag)

A nose up descent with a low airspeed is best.
I did one on my multi engine instrument flight test.  The examiner thought it was great.
You pull back on the power to idle.
Raise the nose like you are wanting to enter a stall.
Let the airspeed wash off.
As it approaches maybe 10 or 15 knots above the stall, you keep the airspeed there by lowering the nose.
Normally when deliberatly entering a stall, you would continue to lift the nose until a wing drops.
But you lower it. To maintain a speed above the stall.
The lift has already reduced enough so that the aicraft will descend.
But it does it with a nose up.
Airliners do it on every landing, but its being done with power applied and so its a gentle desvent.
If you wanted to drop from the sky when you are way too high on an instrument flight test, its best.
You will drop like a stone and have a extremely steep angle.  With very little ground speed.
If you want to get some airspeed back fast, just lower the nose and apply power.  It you want to arrest your descent.  Just slam the power levers forward and you are already in a climb attitude.
Its not for the kind of pilot who is not confident.
But if the plane is part of your body, you will get it naturally.

"The lift has already reduced [...] will descend". A common mistake and a pet peeve:it's not lack of lift that makes you descend, albeit lift is a little bit less in a descent. Hint: lift is also less in a climb !!!

Also, while it is true that descending on the other side of the drag curve (below Vmd) will also achieve a decent rod, and I agree that it is a valuable maneuver in a pilot's toolbox, calling it the best is totally misleading. You are close to stalling, on the speed-unstable part of the drag curve, not something you should take lightly. The (only) advantage is the low speed that allows you to immediately configure and drop the flaps/gear early in the approach, as supposed to a high-speed descent where you now need to level off to slow down before configuring.

This answer describes a procedure for maximum descent gradient, not maximum descent rate. The latter is solely a function of how much gravitational potential energy you can bleed off per unit of time, which is more at high speed.

'Dives' in an airliner should really be avoided at all costs.
A nose-down dive could have the following dangers, just to name a few:

Excessive airspeed, leading to structural integrity issues
The 'pull out' would have a high load factor (think high G force) which would stall the aircraft (or even break it apart)
To 'pull out' without stalling would take a long time to level off - it would be easy to overshoot the 10k feet mark and if there's high terrain...
You would have a cabin-load of vomiting passengers!

The standard emergency descent procedure will get you to a safe altitude quickly enough, with oxygen supplemented.
I'm sorry I can't answer your other questions but I hope I have explained why a dive would not be a viable option.

I don't know whether to upvote or downvote this answer.  I agree with your general point that the 'standard' procedure will get you down more than fast enough aka 7000-8000fpm on a good day, and that diving should generally be avoided in a transport aircraft (FDX705's near-split-S notwithstanding), but it does not answer the original questions, sadly.


text:
What are the differences and benefits between/of time-based vs distance-based separation?
This video suggests a time-based approach to landing aircraft separation is preferable to the distance-based standard commonly used.  It advertises a greater arrival volume at airports, as strong headwinds can delay the time between aircraft landing.
What are the pros and cons for a change in standard?  Under TBS, aircraft would be spaced more closely (distance-wise) on approach during strong headwinds.  Does this present a possible hazard to trailing aircraft if something goes wrong late in the approach (like this runway incursion?)

There is more information available from NATS on the website on Time Based Separation [TBS] and from a very descriptive Infographic on TBS PDF. While Heathrow (EGLL) is the first airport where this is being researched and tested, there are als other works, such as a research paper called Potential Benefits of a Time-based Separation Procedure to maintain the
Arrival Capacity of an Airport in strong head-wind conditions PDF which applies TBS at Charles Des Gaulles (LFPG).
The main focus of using TBS is to increase airport capacity during strong headwind operations, which significantly decrease groundspeed and therefore traffic flow.
None of the papers I have found speak of hazards related to decreasing the lateral distance between flights. The general idea seems to be that the minimal safety gain accompanying lower groundspeeds due to strong headwinds (lower GS means lower closure rate to objects / stationary traffic on ground) can be partially sacrificed and offset by TBS to maintain airport capacity or reduce the impact of the strong headwinds on airport capacity. This sacrifice becomes available since stronger headwinds also aid the dissipation of wake vortex.
The below table is based on own calculations, assuming constant approach speeds.
It should show you how the time to cover a set distance increases with decreasing ground speeds, which means that e.g. it takes longer to cover 3nm to reach the runway threshold. Reducing the lateral separation (the values chosen are deliberately a bit extreme, as none of the papers mentioned a formula to calculate TBS distances) reduces time to cover the distance, but covering 2.5nm at 130 GS is becoming quite close to 3nm at 150 GS.
+-----+-----+-------+-----+
| GS  | 3nm | 2.5nm | 2nm |
+-----+-----+-------+-----+
| 150 |  72 |    60 |  48 |
| 140 |  76 |    64 |  51 |
| 130 |  83 |    69 |  55 |
+-----+-----+-------+-----+

How accurate are speeds measured around airports? This approach relies on the fact that headwinds are constant for the entire approach phase. I understand that wind speeds are well weasured in the vicinity of the airport, but are they also accurately known at the beginning of the approach?


text:
Trailing Edge with Cavity
I have noticed from PAPER "NASA Supercritical Airfoils - Technical Paper 2969" that they mentioned something called "Cavity" merged with the trailing edge.

Although there is no more detail on it of how it works (Coanda effect or winglet effect) but from experimental tests it shows that it has low drag coefficient compared to blunt TE as we see in graph below;

So, my question is why we dont see such design in any recent planes ??

Note: the graphs and the actual text of the documents mentioned in this answer are for some reason contradictory, but since the text in both is consistently referring to 1.0% thick trailing edge airfoil with cavity, I go with the assumption that is correct, even though the graph shows the 0.7% thick trailing edge airfoil with cavity having even smaller coefficient of drag.
The research paper mentioned in the question is availlable here:
NASA Supercritical Airfoils - Technical Paper 2969 (direct link to pdf file)
The first picture showing airfoil sections is from page 48, and second one showing the cd vs. M graph is from page 49 of the document.
Regarding the trailing edge cavity the document states:

(3) small drag reductions through the Mach number range resulted when the 1.0-percent-thick trailing edge was modified to include a cavity in the trailing edge

That portion of the aforementioned document refers to original research from 1971, which is availlable here:
Wind-tunnel investigation of effects of trailing-edge geometry on a NASA supercritical airfoil section
To verify original source, with regards to the trailing edge cavity, the summary of the latter document states:

In addition, small drag improvements were realized when the airfoil with a trailing-edge thickness of 1.0 precent was modified to include a cavity in the trailing edge.

The second paragraph of dicussion section of the document states:

The results of the present investigation show a small, but consistently measurable reduction in drag for the 1.0-percent-thick trailing-edge cavity when compared with the 1.0-percent-thick blunt trailing edge for the 10-percent-thick airfoil.

Furthermore the conclusions state:

Small drag reductions through the mach number range resulted when the 10-percent-thick airfoil with a 1.0-percent thick trailing edge was modified to include a cavity in the trailing edge.

So: the original research did clearly show small reductions in drag for the airfoil with 1% thick trailing edge and a cavity. (emphasis mine)
However, the more recent Nasa Supercritical Airfoils technical paper cited in the question states:

the optimum trailing-edgethickness was found to vary with the maximum thickness of the airfoil and to be somewhat less than 0.7 percent.

So: while the cavity did prove to have small benefits, they were present in a configuration (1.0% thick trailing edge) which was not overall the best possible as per research (less than 0.7 % thick trailing edge).
It is therefore most probable that the best overall choice is to go with the 0.7% thick blunt trailing edge version. Also worth noting is, that while the coefficient of drag may be better for some configuration, other properties of that configuration may well be worse. A single metric is never used to make design choices.

I am very curious as to why the cavity has any efficiency benefit in some cases. There might not be enough research on this topic though. Great answer either way!

@Wyatt that would make a very good question to which I do not currently have an answer for, but I guess the reason is that the cavity affects the mixing of the airflow coming from the top of the wing and the bottom of the wing perhaps by offering a small area for the turbulence to reside in so to say. A blunt or rounded trailing edge will shed Karman vortexes, (Google that), a cavity might prevent it.


text:
What are the heating tubes used during SR-71 airframe manufacturing?
I was watching a YouTube video "Titanium - The Metal That Made The SR-71 Possible" when I stumbled upon this frame (at 12:26).
I could see these heating tubes sort of things under the airframe. What exactly are these and what benefit do they add during the manufacturing process to the airframe?

What video is this out of?

My guess is they do not participate in the manufacturing itself. The SR-71 was mostly made of titanium alloy, so composite material curing should be out of the way. However, the blackbird was built to sustain tremendous the amount of heat stemming from the air friction. These heating tubes could very well be a component of a heating stress test that was used to certificate the aircraft, or to verify a plane before release to the air force

How do you know they are heating tubes?

@CarloFelicione I found the video, edited link into question.

@pericynthion They seemed red, and seem to be radiating heat, hence I concluded they must some sort of heating tubes.

It's basically an open air test oven.
The SR71's skin temperatures averaged around 5-600 deg F, up to 1000 deg F in places.  The titanium structure had to accommodate a lot of thermal expansion from all this heat, and used special skin joints and corrugation of the larger-area skin panels to accommodate the expansion.
The heating system in the clip would have been a test fixture with an array of radiant heating elements to subject a skin assembly to operating temperature to study the effects and validate the design (go to Page 29 of the linked PDF).


text:
What do taxiway lane, taxiway strip and taxiway shoulder mean?
I am developing a game which involves an airport simulation. And I am looking into the general rules that traffic control has for busy airports and am also confused on the terminology of a taxiway.
According to ICAO taxiway widths have 3 types of labeling which is as follows:
Taxiway Lane
Taxiway Strip
Taxiway Shoulder

What is the taxiway shoulder? I am fairly sure the lane is the 2 outer yellow lines from the center  taxiway line right? And the strip is the entire taxiway width, but I am unclear on the shoulder label? I could not find an image that showed what this was.

Your last paragraph should be a separate question,  if this similar question doesn't cover it.

@fooot i'm not sure it does answer it, it doesn't explain which gets priority - the departing plane from jetways etc or the plane already on the move on the taxiways. Unless theres no logical priority and is decided in the moment by traffic control.

Priority is usually given to aircraft ready to taxi, before other aircraft are cleared for pushback. This might be overruled by slot assignments, if the plane pushing back has a significantly earlier slot to make and would need to be sequenced in front of the other aircraft anyway. Too many factors to logically disseminate this.

@Dave I've trimmed your second question about pushback priority because none of the answers below really address it, and it should be a logically separate question anyway. If you ask it as a separate question we can try to get you some answers :)

According to the Skybrary from EUROCONTROL and a UK CAA document on taxiways markings (Visual Aids Handbook UK CAA CAP 637 (2007)), the definitions are:
Taxiway Strip
An area which contains the taxiway and gives protection to aircraft from obstacles and other taxiways.
Image Source: Transport Canada
Taxiway Lane
This one is ambiguous and could not be found citation on, except for a document from the BAZL. Taxilanes or Taxiway Lanes are dashed taxiways, which give guidance to stands and aircraft parking positions.
Taxiway Shoulder
The taxiway shoulder is the paved or unpaved area beyond the double taxiway edge line, indicating that the load bearing capabilities beyond these lines can be different from the taxiway weight allowance.

Take a look at Section 3. Airport Marking Aids and Signs of the FAA's AIM and AIRPORT SIGN AND MARKING – QUICK REFERENCE GUIDE

Good info, the first link seems to be broken now though.


text:
What do the callouts "approaching minimums" and "minimums " mean?
When landing, what exactly do the phrases "approaching minimums" and "minimums" mean in a commercial jet aircraft,  when heard from the onboard cockpit voice.

The "Approaching Minimums" callout is made by the Pilot Monitoring (or, in some cases equipment, the GPWS -- Ground Proximity Warning System) as the aircraft is descending on an instrument approach and has reached an altitude 100 feet above the minimums for that approach -- the Decision Altitude (DA -- typically used for a Cat I ILS, and set as XXX' MSL) or Decision Height (DH -- typically used for a Cat II or Cat III ILS and set as XXX' or XX' on the Radio Altimeter) or Minimum Descent Altitude (MDA -- typically used for a nonprecision approach and set as XXX' MSL).  The response by the Pilot Flying is usually standardized and indicates he is looking outside in order to acquire the visual references he'll need to land.
The "Minimums" callout is made at the minimum altitude, and this is the point that the Pilot Flying has to make a decision -- continue or go around.  His response at this point is again standardized so that the other pilot is entirely clear on the course of action.  His response is usually something like "Landing" or "Continue", or else "Go Around."  Often, the autopilot comes off at this point as well & you hear the horn indicating such on the CVR as well.

Why MSL in this case since airport can easily been above 200' MSL?

For a Cat I ILS, you call minimums off the Baro altimeter, so for a runway at 605' MSL, you'd call "Minimums" at 805' MSL.  That's a DA.  For a Cat III ILS to the same runway, you'd call "Minimums" at 50' RA -- that's a DH.  The DH would correspond to 655' MSL, but the Radio Altimeter is primary because of its accuracy.

@757toga  Making those callouts off of the MDA itself would correspond with a "dive & drive" type of profile; for a constant angle descent approach toward a published MDA, the minimum altitude would have to be raised above the MDA for the reasons you discuss. My carrier refers to that MDA + 50' as the "Derived Decision Altitude" or DDA, which becomes your minimum for the approach. That's what's bugged on the altimeter, that's where the "Minimums" callout is made, and "Approaching Minimums" is made 100' above that.  Since DDA isn't universal, I kept the answer to the more general cases.

"Approaching Minimums" you are about at your minimum descent altitude (MDA) or decision altitude (DA).
"Minimums" means you've arrived at that altitude.
Pilots use those phrases to alert the pilot flying when they're getting close to the ground.  At minimums they will either have the runway environment in sight and decide to continue and land on the runway or they will not have the runway environment in sight and decide to go around.

Approaching minimums is the decision making altitude or minimum altitude ( Generally 100  feet above the minimum altitude ). Captain callout ‘approaching minimums’ in order to decide that they will land on the runway or they will go around, that depends on the Captain. In their final approach if they are going for landing then the other pilot callout “ continue” or else the other pilot callout “Goaround” and then the landing was aborted....the Pilot pushes the thrust levers to its maximum position  in order to get the maximum thrust generated by the engines and then the landing gear was retracted in order to goaround....

This seems to be contradictory with existing answers: Approaching minimums is not for decision making, but to warn that the decision to stop the descent has to be made soon, when reaching minimums (DH/MDA)


text:
How are pilots trained to prepare for crashes?
I once read somewhere that pilots can go to some facilities so get trained for crashes.

I actually went to a facility in New London, CT where they actually
  dunk you in water strapped in the seat of an airplane upside down and
  with your eyes closed in a big pool.

Is there any formal training for the commercial pilots to be prepared for crashes? If yes, how far do they go in training pilots and for what kind of crashes?

Mind sharing the name of the place? You've caught my interest :)

From my research to date it seems that most general aviation and commercial fixed wing pilots are instead trained rigorously in crash avoidance rather than crash escape. Flight attendants and other cabin staff drill regularly in crash preparation and cabin evacuation in several situations (gear-down landing, belly landing, water landing, fires blocking escape doors X, Y and Z, etc) but in an emergency, the job of the people behind the yokes is to first make sure the plane gets back on the ground in as close to one piece as possible; nobody's walking away from a nose-down dive into a mountain.

General aviation pilots are pretty much on their own for seeking out this kind of training. There are companies that do the underwater bit, and I'd bet there are companies that do smoke chamber egress training in stuff like a Gulfstream or Citation mock-up (for the light GA crowd it's generally assumed you know where the doors are in a 4-seat Cessna or Piper…)

I've seen pictures of this sort of training for helicopter underwater emergency training.
Training link
This is given to offshore oil rig crews, who will be passengers on the helicopters, as well as the pilots who will be flying them.
As offshore crews fly so frequently in helicopters, it's worth the time giving them this sort of emergency training.
I've never heard of it being used for fixed wing plane crews though.

I saw an episode of "Dangerous Flights" where the flight crew prepared for a trans-Atlantic ferry flight with training similar to what the question described. They were ferrying a single-engine Cessna.

They send you up in a small airplane and turn off the engine. Just kidding.
There is no formal training, except in the use of standard emergency equipment such as evacuation slides and the emergency oxygen system.
Every aircraft has an elaborately detailed set of emergency procedures which are kept in binders (although this is shifting to iPads). When something bad happens, you are supposed to turn to the relevant section of the binder (there are quick reference tabs) and follow the instructions. In theory, you are supposed to memorize all the procedures, but in practice most pilots just know the critical ones, like fires and engine failures. Even if you think you have the procedure memorized, you are still supposed to use the checklist.
One problem with simulating emergencies is that it is dangerous. For example, the FAA used to mandate spin training for all pilots. Then, years later, they found out more people were getting killed in the spin training, than were getting killed in real, actual spins. That put an end to the spin training.


text:
How are cruise missiles different from ballistic missiles?
Cruise missiles and ballistic missiles are used by many nations as offensive and defensive technology. How do cruise missiles and ballistic missiles maneuver, and what are the differences between the basic principles of these maneuvers?

I have rolled back your edit and removed aircraft-design as a tag. While the tag control surfaces is appropriate as they do exist on missiles, a missile is not an aircraft.

I tagged it after reading this article : https://en.wikipedia.org/?title=Aircraft#Aerodynes

What do aerodynes have to do with missiles?

Read that. The last line tells what aerodynes have to do with missiles (in some cases)

I DID read it, hence why I am curious how you believe missiles are a type of aircraft. Heavier-than-air types are characterised by one or more wings and a central fuselage.

Sorry, wrong link. The right link : https://en.wikipedia.org/?title=Aircraft#Heavier-than-air_.E2.80.93_aerodynes

A pure rocket is not usually regarded as an aerodyne, because it does not depend on the air for its lift (and can even fly into space); however, many aerodynamic lift vehicles have been powered or assisted by rocket motors. Rocket-powered missiles that obtain aerodynamic lift at very high speed due to airflow over their bodies are a marginal case.

Let us continue this discussion in chat.

Neither a cruise missile nor a ballistic missile is a defensive weapon.  Their design purpose is strictly offensive.  A surface to air missile is  mostly a defensive weapon, by design and usage.   Your question needs to be corrected to remove that incorrect premise/assumption. "used as offensive/defensive weapons" is wrong.  "Used as weapons" is correct.

@SentryRaven  Have to disagree - a missile is indeed an aircraft, though I suspect you meant to say that it is not an aeroplane, which is also debatable, particularly with cruise missiles.

Cruise Missile :

Uses thrust for the whole trajectory
Uses aerodynamic forces by moving control surfaces to move. May use thrust vectoring

Ballistic Missile:

Uses thrust to reach very high altitude. After that, no thrust, only potential energy is used and converted to speed.
Uses aerodynamic forces (for a limited extent) to move by deflecting control surfaces.

The boost phase in a ballistic missile is used not only a gain altitude, but also (and primarily) to gain speed. After the boost phase, they follow a ballistic trajectory, very much like a bullet, an artillery shell, or an arrow would. The horizontal component of the velocity will generally be at its maximum at the end of the boost phase, though the absolute value of the vertical component might be higher at impact in some designs.

Could you perhaps expand on your answer to explain the advantages of each?

A cruise missile is rocket or jet powered and flies to its target within the atmosphere, using lift to stay up. Most have wings, although a few may use lifting body designs. They maneuver using control surfaces on the wings and tail like an airplane. Mission profiles can include big course changes, to evade air defenses, or to hug terrain to stay hidden. They can be launched from fixed ground positions but most are launched from mobile platforms. They tend to have shorter ranges than ballistic missiles.
A ballistic missile is a rocket that powers its way out of the atmosphere and coasts in an arc, re-entering the atmosphere before hitting its target. They have little maneuvering capability, once the boost phase is done it's all down to physics. Some warheads are able to maneuver a bit in re-entry in order to hit a pinpoint target, others are just rocks at that point. The largest ones are launched from fixed positions like missile silos but smaller ones are mobile.

Do SRBMs actually leave the atmosphere? I know ICBMs obviously do, but I didn't think leaving the atmosphere was a requirement for being a ballistic missile. As far as I know, 'ballistic' just means the it follows an unpowered, ballistic trajectory after the end of the boost phase (i.e. a path arced by gravity like an arrow or a bullet.)

No, leaving the atmosphere is not necessary. SRBMs like the ATACMS that have been in the news recently, reach 50-60 km, roughly half the Kármán line.

Cruise missiles have rocket or jet engines that are powered during the entire flight. It allows the missile to cruise low through the atmosphere, sometimes just above ground level. Lift and guidance of the missile are achieved by aerodynamic forces.
Ballistic missiles on the other hand are not powered during most of their flight. During the launch they are given a high initial velocity and then coast throughout most of their flight. Their flight path is by approximation parabolic. Ballistic missiles are guided during brief periods of their flight, aerodynamically and/or by thrust vectoring. Intercontinental Ballistic missiles go into a suborbital paths and spend a considerable part of their trajectory outside the atmosphere.

A ballistic missile is one which flies in a ballistic trajectory.  They usually are composed of a solid rocket booster stage lifting a warhead and guidance section aloft as a payload .  After the booster burns out, the payload section continues on a ballistic trajectory to the target.  Sometimes the booster motor is jettisoned after burnout.
Ballistic missiles vary in size and capability from battlefield types such as the ATACMS missile fired from the M270 MRLS, to regional range types such as the MGM-31 Pershing missile to intercontinental range types such as the Minuteman III.  Warhead types can range from conventional aerial explosives like Tritonol 80/20 to chemical, nuclear or thermonuclear types.  Some ballistic missile contain multiple and independently targeted warheads on a warhead bus.
Cruise missiles are essentially guided flying bombs - unmanned heavier than air aircraft capable of sustained, powered flight from launch until it reaches the target.  They range in speed from subsonic to supersonic.  Propulsion is generally provided by small gas turbine jet engines, though some of the newer, supersonic types are powered by solid fuel ramjet engines.  Warheads carried are conventional, chemical or nuclear.  Some of the best known cruise missiles are the AM39 Exocet anti-ship missile or the BGM-109 Tomahawk missile.

Difference between cruise and ballistic missiles
There are some important differences between cruise and ballistic missiles. These are:

Ballistic missiles follow an arc-like trajectory and are launched
from the land or sea
They usually carry a nuclear warhead and are
very heavy
They rely on Earth’s gravity to fly down once launched
They have much larger range
Cruise missiles can also be launched from air and fly within Earth’s atmosphere
They have their own engines and wings to strike the target
They can be supersonic or sub-sonic and are highly accurate
They usually carry conventional warheads although some cruise missiles can also be equipped with nuclear warheads

In both cases, these missiles are guided. That is, the flight path is pre-determined and very small alterations in flight are possible, if at all.

authors: Костя Дряхлов


text:
Do small airfields provide ATIS? If not, what weather reporting service is available?
Would a very small airfield or airstrip be considered to be a 'terminal' and have Automatic Terminal Information Service (ATIS)? Or would it just have minor weather reporting?
As in, would it make sense to provide ATIS (Automatic 'Terminal' Information Service) for a very minor airstrip? How does an airstrip qualify as being a 'terminal' to require those services?

There is no minimum definition of a "terminal" in and of itself. The "destination terminal" of a flight is simply its planned endpoint. That's usually, but not always, a man-made complex designed to facilitate human flight, which we call an airport. However, you can file a VFR flight plan to fly out to a friend's fallow field in BFE, miles from any airfield listed on a sectional:

It's then your responsibility, as it always is in VFR, to ensure you can operate the plane safely at all times, including getting the plane on the ground and then back up in the air without causing personal injury, property damage, infringing private property rights, violating noise ordinances, etc.
Sectional diagrams use the term "airport" to refer to any place that is registered with the FAA to be used for the purpose of aircraft takeoffs and landings. These places may be more specifically called airstrips, airfields, air parks, aerodromes etc to indicate relative size, construction, ownership or facilities.
The only requirements for an airport to be documented by the FAA and appear on a sectional are:

The location must meet minimum guidelines specified in the Airport Certification Manual, including land grading for smoothness and drainage, obstruction/obstacle clearance in three dimensions, and minimum safety markings and wind/traffic pattern indicators that are necessary to support aircraft takeoffs/landings at the location (really the only thing every airport requires along these lines is a windsock; everything else is provided as needed for the specific location or as desired by the field's users). This usually requires a minimum amount of maintenance/upkeep by its owner for the purpose, even if it's just a grass field (it would have to be regularly mown and weeded to remove certain spiky or wood-stemmed plants, for instance).
The location must be registered with the FAA by its owner/manager for this purpose (they can register it as a reserved/private airfield, and then only limited information will be given on the sectional, primarily as an advisory that the location is available for emergency landings).

That's all there is to it. Besides a windsock which is the absolute minimum, no minimum facilities must exist; even the traffic pattern/landing direction indicators are optional if traffic can always use a left-hand pattern and determine the runway approach from the windsock. Rhome Meadows Airport (T76) between Fort Worth and Decatur, TX is a grass strip, with no lights, no tower, no fuel, no hangars, and the displaced threshold on the south end is marked with two white painted tires (no threshold markings to the north). Nearby Heritage Creek Airstrip is only slightly better, with low-intensity runway edge lights. Despite this, both are fairly active for unimproved strips, with about nine flights a day involving each one in some way (TO/L, T&G).
Here's the airport section of the legend for FAA sectionals:

You can see that there's a wide array of symbology available to indicate at a glance what the facility offers; control tower or no, length and configuration of hard surface runways if any, usage type, presence of FBOs for fuel/maintenance, navigational aids, and radio information including ATIS, AWOS, ASOS, control towers, UNICOM etc. Obviously a control tower needs a radio frequency, but there is no requirement that a towered facility have ATIS. ATIS is usually found at towered airports as its purpose is to reduce controller workload, but nontowered airports can have ASOS/AWOS stations which provide practically the same information regarding weather, without the superfluous runway information (at nontowered airports, the pilots usually determine the approach/departure direction). If an airport has no reporting whatsoever, you would usually tune to the nearest listed AWOS/ASOS.

No, small airports almost never have ATIS. Many do, however, have an AWOS or ASOS. However, this is also not a requirement and many very small and/or private fields don't have any weather reporting at all. If any such system is present, its radio broadcast frequency will be listed on the sectional charts. When no weather reporting service is available at a particular airfield (either due to there not being one there or it being out-of-service,) pilots will generally just tune in to the weather reporting frequency of another nearby airport that is likely to have sufficiently similar weather.
The word 'terminal' is used in aviation to describe any type of airfield, regardless of its size. However, the presence of the word 'terminal' in the name for ATIS is not meant to imply that all terminals have ATIS, but only that all ATIS's are associated with a terminal.
AWOS (Automated Weather Observing System) and ASOS (Automated Surface Observing System) systems, as their names imply, automatically monitor local weather conditions. They then produce a computer-generated voice that plays this information in a loop on a radio frequency that will be stated in the A/FD entry for the airport and listed on the sectional charts.
ATIS includes weather information like an AWOS or ASOS, but also includes information about the airport itself, such as which runway(s) are active, which approaches are available, and anything else the local air traffic controllers want pilots to know before they contact ATC. This is not needed at small airports because they don't have air traffic controllers and pilots just choose which runway they're going to use based on current traffic and weather conditions and tell each other about it on the radio. It's also not present at some smaller airports that do have towers because the controller workload is low enough already that it isn't needed. At larger airports, though, having ATIS available helps to prevent controllers from having to waste time repeating the same information to every single pilot approaching the airport and also helps to free up the radio frequencies used by the controllers, allowing pilots and controllers to relay information to each other more quickly and efficiently.
For example, Livingston Municipal Airport is a small airport near where I live that has an AWOS-3 transmitting on 126.175 MHz:

The smaller nearby Jackson County Airport, however, has no weather observation facilities. Aircraft approaching this airport would probably just listen to the weather report from Livingston or another nearby airport:

The much larger nearby Nashville International Airport does have ATIS service operating on 135.1 MHz:

Airstrips provide at least a wind sock (or wind cone) to indicate direction and strength of the wind at ground level.
A wind sock is required to operate even the tiniest strip, and as such provides the minimum level of weather information available - provided the pilot is close enough to be able to see it clearly.
The specifications of this information source are discussed in the answers to this question.
Note the FAA specification available here.

In Germany, most airfields that are equipped or certified for IFR operations will have an ATIS. In those cases were an airfield is not equipped with an ATIS, all weather information produced by the certified meteorological personnel at the airfield will be provided on the AFIS (Aerodrome Flight Information Frequency) frequency upon request.

(Image Source: AIP Germany AD EDGS)
For all airfields that neither have certified meteorological personnel or equipment, the weather information will be rudimentary, such as winds only, but no QNH, precipitation or cloud observation. ASOS or AWOS are not used in Germany.